Metallocene catalyst systems are extensivily used in a variety of polymerization systems. Typically, these systems include two components, the metallocene component and activator component. A problem associated with metallocene catalyst systems is the presence of impurities which detrimentally effect catalyst performance and polymer particle morphology. Among the most common impurities associated with the metallocene component are metal salts which are either formed or remain unreacted during the metallocene synthesis. The detrimental effect of these impurities is generally not recognized.
Removing these impurities or preventing their formation during metallocene synthesis presents a number of difficulties such as reduced yield of metallocenes, use of large volumes of solvent, and an overall increase in expense. For example, U.S. Pat. No. 5,302,733 describes a lengthy synthesis involving filtration, extraction, separation, evaporation, and/or recrystallization steps to isolate racemic metallocene isomers of interest. The metallocene compound recovered is reported as being substantially free of alkali metal salt by-product. Removing metal salts and other contaminants after metallocene compound synthesis would be difficult because many metallocene compounds along with the impurities typically associated with such compounds are sparingly soluble or less in hydrocarbon solvents thus making purification impractical. Therefore, there exists a need for a simple post synthesis method of purification which enhances polymerization performance and is cost effective.